Differential throttling of rocket engines for a high performance vehicle such as rocket powered SSTO is studied. For both powered ascent and landing of a vertical landing rocket vehicle, taking into account the attitude motion of the vehicle in atmospheric flight, the necessary restoring moments are evaluated. These were converted to the throttling requirement for each engine in terms of both static and dynamic characteristics, and rocket firing tests were carried out. Engine throttling was done by control of the hot turbine working fluid. Stable static throttling capability was demonstrated from 30 % to 100 % of its maximum thrust level. The frequency response of the engine thrust modulation was investigated and the correspondence between the simulation-model derived dynamic response and the real behavior was verified. Finally closed-loop engine thrust control by connecting a pressure signal from the engine combustion chamber to the throttling valve was tested for better dynamic response. The expected improvement was achieved in the frequency range concerned. As a result of the study, good controllability for attitude control by applying differential thrust of the primary propulsion was demonstrated.

References:

SSTO Propulsion Design

A Concept of Reusable Sounding Rocket with Enhanced Maneuverability and Operability